The present disclosure relates to polymeric tubular conduit for insertion into the body and methods of manufacturing the same. The conduit comprises a polymeric material combinable with other suitable components for cannulation in medical applications.
Cannulation is a process of introducing a cannula into the body of a patient (e.g., body cavity, duct or blood vessel, organ, or the like) for the introduction or removal of fluids (e.g., blood, medications, or air) or devices (e.g., catheter). The cannula may be used for short periods of time (e.g., during surgery) or for extended periods (e.g., extracorporeal membrane oxygenation (ECMO)). For example, surgical procedures related to a patient's heart may require the blood flow through the heart be by-passed in favor of an extracorporeal circulation device (e.g., a heart lung machine). A heart lung machine can be used to circulate and oxygenate blood while the patient's heart is being repaired. The heart lung machine is coupled to the patient's vascular system through specialized conduits called cannulae (plural of cannula). Cannulae adapted to receive blood from the body and transmit the blood to the heart lung machine are called venous cannulae. Cannulae adapted to return blood from the heart lung machine back to the body are called arterial cannulae.
Cannulae were used in human heart bypass surgeries as early as the 1950's. Since then, the overall designs of the most widely used arterial and venous cannula have not changed dramatically. Historically, cannulae are semi-rigid components often made of polyvinyl chloride (PVC) secured by sutures in the patient's arterial and venous structures. When a cannula is made from PVC, plasticizers are often used to provide the PVC, a highly rigid polymer without plasticizers, with the appropriate properties. A plasticizer is an additive that increases a polymer's flexibility, workability, and ability to be elongated. Plasticizers essentially lubricate the polymer chains in a polymer composition so that the intermolecular forces between and along the chains are reduced. This loosening of the intermolecular forces allows the polymer chains to slide across each other more freely.
Most plasticizers are organic compounds with elevated boiling points, low vapor pressures, and poor water solubility. For example, ester phthalates are regularly used because of their particular effectiveness in lubricating polymeric materials. Currently, two commonly used plasticizers are di-2-ethylhexyl phthalate (DEHP) and di-isononyl phthalate (DINP) both of which are phthalates. These plasticizers are routinely used with PVC to make a variety of products. For example, many medical products, toys, and baby products include components comprising PVC and a plasticizer like DEHP. The incorporation of the plasticizers into PVC products provides the composition with the soft, flexible, and supple feel that is associated with these products.
Plasticizers can be compounded with the polymeric materials with which they are used. Most plasticizers do not react to form any chemical bonds with the polymer. Essentially, the plasticizer is dissolved within the polymeric material because of the favorable physical interactions between the polymer and the plasticizer. The favorable physical interactions typically prevent the plasticizer from leaching out of the polymer. While plasticizers are typically not water soluble, they are soluble in non-polar solvents and are known to be slightly soluble in blood and other bodily fluids. Accordingly, in a cannula manufactured with a plasticizer an amount of plasticizer may be leached out in vivo and become dissolved in bodily fluids. For example, a publication by Peck and Albro, Environmental Health Perspectives Vol. 45, pp. 11-17, 1982, found that DEHP plasticizer from a PVC/DEHP blood bag accumulate in plasma during 4° C. liquid whole blood storage at a rate of approximately 1 mg/unit/day. There has been extensive research and debate surrounding the toxicological impact of DEHP in biological fluid. The results have been inconsistent and there is not a clear answer as to whether and to what extent such plasticizers may be a health risk to patients. It would be desirable to produce a cannular device which is free of plasticizers yet will provide the desired properties of flexibility, workability and ability to be elongated.